TURN MUSIC OFF

This has apparently nothing to do with FCP.

If I understand correctly, you are saying that "music files" open in Music.

Files like mp3, m4a, wav, aifc open in Music by default.

If you want them to open in Quicktime Player, that's easy. Select one of each in the Finder, press Command-I to open the Info window; under "Open With", change to Quicktime Player; click Change All.

Note: you have to do this once per file extension - e.g., one mp3, one m4a, etc.

Opens up where? When you export a file you can see what opens it, or not open it at all.

This is the export Settings window in FCP.

You can set whatever you want to open an exported file. What are you doing and what are you seeing in the application?